Best 4 person all caster/priest group

[fortior]

I think there are situations where you'd want both a cleric and a shaman, but the question of 'best 4 man group' cannot be answered without knowing the context, since each of the following meaningfully alters which classes' abilities are top tier

- the goal (xp, plat, loot, 'hardest target killed', specific quests, etc)
- real world or in a vacuum, aka is there competition (FTE or clearing wise), do you need the ability to do many different camps if yours is taken
- does the group need to act like a cohesive group

The OP is vague on all of this which is actually a benefit, because now you can look at different sets of contexts and see where some classes shine.